The overall goals of the proposed research are: 1) to examine the effects of physical exercise on tissue lipoprotein lipase (LPL) activity of rats, and 2) to investigate, in vitro, the factors which participate in the regulation of LPL activity. Sustained high levels of plasma triglycerides have been implicated in the development of atherosclerosis and ischaemic heart disease. In response to physical exercise, plasma triglyceride levels rapidly decrease to normal values contributing, therefore, to the prevention of these pathological conditions. The mechanisms whereby exercise produces this reduction in plasma triglyceride levels are not yet completely understood. The results of our studies suggest that muscle LPL may be implicated in this process. Thus, physical exercise by producing significant increases in the red fiber type muscles LPL activities may greatly increase the rate of triglyceride removed from circulation. Knowledge of the factors involved in the regulation of LPL activity is, therefore, of great importance since by changing the enzyme activity in various tissues it may be possible to control the levels of plasma triglycerides in a variety of pathological conditions.